The present invention relates to a controller for an internal combustion engine.
In an internal combustion engine mounted on a vehicle such as an automobile, an exhaust passage is provided with a catalyst for purifying exhaust gas. The catalyst removes NOx, HC, and CO from the exhaust gas flowing through the exhaust passage. To effectively remove the three components from the exhaust gas, the catalyst has an oxygen storage function, and the amount of fuel injected into an internal combustion engine is controlled so that the air-fuel ratio of an air-fuel mixture in a combustion chamber of the engine is adjusted to stoichiometric air-fuel ratio.
The oxygen storage function of the catalyst functions to draw oxygen from the exhaust gas into the catalyst and remove oxygen from the catalyst and emit the oxygen into the exhaust gas in accordance with the concentration of oxygen in the exhaust gas passing through the catalyst.
More specifically, when the oxygen concentration of the exhaust gas is higher than a value obtained when an air-fuel mixture having the stoichiometric air-fuel ratio is combusted in the combustion chamber, that is, when an air-fuel mixture having an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio is combusted in the combustion chamber, the catalyst stores oxygen from the exhaust gas passing through the catalyst due to the oxygen storage function of the catalyst. In contrast, when the oxygen concentration of the exhaust gas is lower than the value obtained when the air-fuel mixture having the stoichiometric air-fuel ratio is combusted in the combustion chamber, that is, when an air-fuel mixture having an air-fuel ratio that is richer than the stoichiometric air-fuel ratio is combusted in the combustion chamber, oxygen is removed from the catalyst and emitted into the exhaust gas due to the oxygen storage function of the catalyst. Hereafter, in the description, the state “leaner than the stoichiometric air-fuel ratio” is simply referred to as “lean”, and the state “richer than the stoichiometric air-fuel ratio” is simply referred to as “rich”.
The three components, namely, NOx, HC, and CO, may be effectively removed from the exhaust gas when a catalyst has the oxygen storage function and the fuel injection amount of the internal combustion engine is controlled so that the air-fuel ratio of the mixture in the combustion chamber of the engine is adjusted to stoichiometric air-fuel ratio.
More specifically, when the air-fuel ratio of the mixture in the combustion chamber is shifted to a lean state, the oxygen concentration of the exhaust gas passing through the catalyst becomes higher than a value obtained when the stoichiometric air-fuel mixture is combusted in the combustion chamber. Thus, the catalyst stores oxygen from the exhaust gas passing through the catalyst, and NOx is reduced in the exhaust gas. In contrast, when the air-fuel ratio of the mixture in the combustion chamber is shifted to a rich state, the oxygen concentration of the exhaust gas passing through the catalyst becomes lower than the value obtained when the stoichiometric air-fuel mixture is combusted in the combustion chamber. Thus, oxygen is removed from the catalyst and oxidizes HC and CO in the exhaust gas.
Therefore, even when the air-fuel ratio of the mixture in the combustion chamber is shifted between a rich ratio and a lean ratio, for example, as the air-fuel ratio approaches the stoichiometric air-fuel ratio, the three components, namely, NOx, HC, and CO, are effectively removed from the exhaust gas as described above.
In the so-called idling reduction control, an auto-stopping process is performed when the internal combustion engine is idling, and an auto-restarting process is performed when the engine is automatically stopped. When the idling reduction control is executed and fuel injection is stopped after the auto-stopping process is started, the inertially rotating engine sends air to the catalyst through the exhaust passage. Thus, during the inertial rotation of the engine, the amount of oxygen stored in the catalyst increases. Under this condition, the auto-restarting process is performed on the engine.
When the engine runs after the auto-restarting, if the oxygen storage amount of the catalyst is excessively increased, the NOx removal performance of the catalyst deteriorates. In this regard, Japanese Laid-Open Patent Publication No. 2002-327640 discloses a technique in which the amount of fuel injected into the internal combustion engine is increased and corrected after the auto-restarting process is started. When the air-fuel ratio of the mixture in the combustion chamber is adjusted to a rich state through such an increase correction of the fuel injection amount, HC and CO increase in the exhaust gas. To oxidize HC and CO, oxygen is removed from the catalyst. Consequently, the oxygen storage amount of the catalyst is gradually decreased. This limits deteriorations in the NOx removal performance of the catalyst that would occur when the oxygen storage amount is excessively large.
During the inertial rotation of the engine from when the auto-stopping process is started to when the engine is completely stopped (engine rotational speed reaches zero), the total amount of intake air of the engine is generally constant. Thus, in the same manner, during the inertial rotation of the engine, the amount of oxygen stored in the catalyst is generally constant. However, at a point of time when the auto-stopping process is started, the oxygen storage amount of the catalyst would vary in accordance with the engine running state until the auto-stopping process is started and thus is not necessarily constant. This forms variations in the oxygen storage amount of the catalyst at a point of time when the auto-restarting process of the engine is started. Such variations may cause the increase correction amount for the fuel injection amount to have an improper value after the auto-restarting process is started.
After the auto-restarting process is started, when the increase correction amount of the fuel injection is excessively large relative to the oxygen storage amount of the catalyst, the oxidization of HC, CO in the exhaust gas is not completed depending on the removal of oxygen from the catalyst. This deteriorates the performance of the catalyst for removing HC, CO. In contrast, after the auto-restarting process is started, when the increase correction amount of the fuel injection is excessively small relative to the oxygen storage amount of the catalyst, the removal of oxygen, which is used to oxidize HC, CO in the exhaust gas, from the catalyst is decreased. This hinders reduction of the oxygen storage amount in the catalyst and deteriorates the NOx removal performance of the catalyst.
It is an object of the present invention to provide a controller for an internal combustion engine that appropriately maintains the exhaust purification performance of a catalyst by a correction that increases a fuel injection amount when an auto-restarting process is performed on the internal combustion engine.
To achieve the above object, a controller for an internal combustion engine mounted on a vehicle is provided. The engine includes an exhaust passage provided with a catalyst. The controller includes a processor. The processor is configured to perform an auto-stopping process on the engine when the engine is idling, perform an auto-restarting process on the engine when the engine is automatically stopped, correct an amount of fuel injected into the engine so that the fuel injection amount of the engine is increased by a correction amount after the auto-restarting process is started, and change the correction amount in accordance with an amount of oxygen stored in the catalyst at a point of time when the auto-stopping process is started.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.